Generally, a surface of a solid body formed of a metal or a polymer has inherent surface energy, which is shown by a contact angle between the solid body and a liquid when the liquid material contacts the solid material. When the contact angle is less than 90°, hydrophilicity in which a sphere shape of a water drop is lost on a surface of the solid body to wet the surface is shown. In addition, when the contact angle is greater than 90°, hydrophobicity in which the sphere shape of the water drop is maintained on the surface of the solid body to run on the surface is shown. As an example of hydrophobicity, a water drop runs on the surface of a leaf of a lotus flower flows without wetting the leaf.
Further, when the surface of a solid body is processed so as to have slight protrusions and depressions, the contact angle of the surface may vary. That is, when the surface is processed, the hydrophilicity of a hydrophilic surface with a contact angle that is less than 90° may increase, and the hydrophobicity of a hydrophobic surface with a contact angle that is greater than 90° may increase. The hydrophobic surface of the solid body may be variously applied as follows. The hydrophobic surface can be applied to a condenser of an air conditioning system to enhance condensing efficiency. When the hydrophobic surface is applied to a drink can, the residue can be completely removed from the can and thus a recycling process of the can may be simplified. Further, when the hydrophobic surface is applied to a window glass of a vehicle, it can prevent the window glass from being steamed up when there is a difference between an indoor temperature and an outdoor temperature. When the hydrophobic surface is applied to a ship, the ship can exhibit a higher impellent force using the same power. Furthermore, when the hydrophobic surface is applied to a dish antenna, it can prevent snow from covering a surface of the dish antenna. When the hydrophobic surface is applied to a supply tube, a fluid transfer rate and a fluid transfer speed can be improved. Accordingly, since a tube may not be obstructed by foreign materials, cholesterol may not be accumulated in an artificial blood vessel, and an inside of the tube may not be corroded and water therein may not be polluted. In addition, efficiency of a pump increases since the water flow rate increases. Further, when the above characteristics are applied to a micro channel of a lab-on-a-chip, fluid in a channel may be appropriately transferred.
However, technology for varying the contact angle of the surface of the solid body in response to a specific purpose has depended on a microelectromechanical system (MEMS) process applying a semiconductor fabrication technology. Therefore, this technology is generally used for a method for forming nano-scaled protrusions and depressions on the surface of the solid body. The MEMS process is an advanced mechanical engineering technology applying semiconductor technology. However, the apparatus used for the semiconductor process is very expensive.
In order to form the nano-scaled protrusions and depressions on a surface of a solid metal body, a variety of processes, which cannot be performed under a normal working environment, such as a process for oxidizing the metal surface, a process for applying a constant temperature and a constant voltage, and a process for oxidizing and etching using a special solution, must be performed. That is, in order to perform such processes, a specifically designed clean room is required and a variety of expensive apparatuses for performing the processes are necessary.
Furthermore, due to a limitation of the semiconductor process, a large surface cannot be processed at once. As described above, according to the conventional technology, the process is very complicated and it is difficult to mass-produce the products. Furthermore, the cost for producing the products is very high. Therefore, it is difficult to apply the conventional technology.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.